I. Field of the Invention
The present invention relates generally to the modification and control of the temperature of the body. More particularly, the invention relates to a method for controlling body temperature by heat transfer to a balloon.
II. Description of the Related Art
Organs in the human body, such as the brain, kidney and heart, are maintained at a constant temperature of approximately 37xc2x0 C. Hypothermia can be clinically defined as a core body temperature of 35xc2x0 C. or less. Hypothermia is sometimes characterized further according to its severity. A body core temperature in the range of 33xc2x0 C. to 35xc2x0 C. is described as mild hypothermia. A body temperature of 28xc2x0 C. to 32xc2x0 C. is described as moderate hypothermia. A body core temperature in the range of 24xc2x0 C. to 28xc2x0 C. is described as severe hypothermia.
Patients may require pre or post-operative cooling for a variety of reasons, including, for example, treatment of a malignant hypothermia crisis and induction of therapeutic hypothermia for neurosurgery.
Catheters have been developed which are inserted into the bloodstream of the patient in order to induce total body hypothermia. For example, U.S. Pat. No. 3,425,419 to Dato describes a method and apparatus of lowering and raising the temperature of the human body. The Dato invention is directed towards a method of inducing moderate hypothermia in a patient using a metallic catheter. The metallic catheter has an inner passageway through which a fluid, such as water, can be circulated. The catheter is inserted through the femoral vein and then through the inferior vena cava as far as the right atrium and the superior vena cava. The Dato catheter has an elongated cylindrical shape and is constructed from stainless steel.
Other less cumbersome catheters have been developed to provide cooling intravascularly. For example, a heat transfer element such as disclosed in U.S. Pat. No. 6,096,068, incorporated herein by reference in its entirety, may be placed in the feeding artery of an organ to absorb or deliver the heat from or to the blood flowing into the organ. The transfer of heat may cause either a cooling or a heating of the selected organ. The heat transfer element is small enough to fit within the feeding artery while still allowing a sufficient blood flow to reach the organ in order to avoid ischemic organ damage. By placing the heat transfer element within the feeding artery of an organ, the temperature of the organ can be controlled with less of an effect on the temperature of the remaining parts of the body. A similar heat transfer device, which is employed for whole body cooling and which may be disposed in the venous vasculature, is disclosed in U.S. application Ser. No. 09/373,112, also incorporated by reference in its entirety.
While the previously mentioned techniques provide significant thermal control, they require the insertion of a catheter into the vascular system to induce heat transfer between the catheter and the blood stream. This is a relatively invasive procedure, which has an associated level of risk.
Accordingly, it would be desirable to provide an effective, less invasive method and apparatus for heating or cooling all or part of a patient""s body. It would also be desirable to provide an effective, less invasive method and apparatus for heating or cooling all or part of a patient""s body that could be employed in emergency situations, such as on an ambulance.
The present invention provides a method and apparatus for heating or cooling at least a selected portion of a patient""s body. The invention provides a method and device to transfer heat to or from the at least a selected portion in an efficient manner. The device has a high degree of flexibility and is collapsible, thereby affording an easy insertion procedure. The device allows a high surface area to increase heat transfer.
The method begins by inserting a balloon catheter through the anus into the colon of the patient. The system includes a supply lumen and an at least partially inflatable return lumen. The return lumen is coupled to the supply lumen so as to transfer working fluid between the two. A heated or chilled fluid is conducted through the supply lumen of the catheter and into the balloon. The fluid is evacuated from the balloon through the return lumen of the catheter. Heat transfer occurs between the working fluid and the tissue of the colon.
Variations of the system may include one or more of the following. The supply lumen and the return lumen may be made of a flexible material such as latex rubber or other plastics. The radii of the supply and return lumens may decrease in a distal direction such that the supply and return lumens are tapered when inflated. A wire may be disposed in the supply or return lumens to provide shape and strength when deflated.
The thickness of the return lumen, when inflated, may be less than about xc2xd mil. The length of the supply lumen may be between about 5 and 150 or more centimeters.
The system may further include a coaxial supply catheter having an inner catheter lumen coupled to the supply lumen and a working fluid supply configured to dispense the working fluid and having an output coupled to the inner catheter lumen. The working fluid supply may be configured to produce a pressurized working fluid at a temperature of between about xe2x88x923xc2x0 C. and 50xc2x0 C. Higher or lower temperatures may be employed if desired.
In another aspect, the invention is directed to a method of changing the temperature of a body by heat transfer. The method includes inserting an inflatable heat transfer element into the colon of a patient and inflating the same by delivering a working fluid to its interior. The temperature of the working fluid is generally different from that of the colon tissue. The flexible, conductive heat transfer element preferably absorbs more than about 500 watts of heat.
The circulating may further include passing the working fluid in through a supply lumen and out through a return, coaxial lumen. The working fluid may be a liquid at or well below its boiling point, and furthermore may be aqueous.
Advantages of the invention include one or more of the following. The design criteria described above for the heat transfer element: small diameter when deflated, large diameter when inflated, high flexibility, and enhanced heat transfer rate through increases in the surface of the heat transfer element facilitate creation of a heat transfer element which successfully achieves patient cooling or heating. The process is relatively non-invasive. In addition, rapid cooling or heating to a precise temperature may be achieved. Further, treatment of a patient is not cumbersome and the patient may easily receive continued care during the heat transfer process. The device and method may be easily combined with other devices and techniques to provide aggressive multiple therapies. The device may employ the ubiquitous saline as a working fluid. The device has a very high surface area, particularly as the length may be on the order of a meter and the diameter on the order of 0.1 meters. Use of the device may not require the sedation of the patient. The power transferred during cooling could be as high as 600 to 1000 watts. Other advantages will become clear from the description below, including the figures and claims, as well as from the above.